Process for the oxidation of ethylene to ethylene oxide



Patented July 19, 1955 nice PROCESS FOR THE OXIDATION OF ETHYLENE TO ETHYLENE OXIDE George Caiingaert, Geneva, N. Y., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Original application December 9, 1950, Serial No. 200,127. Divided and this application August 22, 1951, Serial No. 243,745

2 Claims. (Cl. 260348.5)

This invention is a division of my co-pending application, Serial Number 200,127, filed December 9, 1950, now Patent No. 2,593,100. This invention is directed to a process for the oxidation of ethylene using silver deposited on a spinel support.

Ethylene oxide is an important chemical intermediate, being employed commercially in many processes. For example, acrylonitrile can be manufactured by treating ethylene oxide with hydrogen cyanide. Hydrolysis of ethylene oxide to ethylene glycol results in an important antifreeze compound. Likewise, from ethylene glycol can be prepared glycol dinitrate for dynamite. Furthermore, ethanolamines, resins, polymers, aldehydes and glycol ethers can be manufactured from ethylene oxide. By treating the oxide with alkyl phenols important detergents can be manufactured, etc. Finally, ethylene oxide finds commercial use itself as a solvent and fumigant.

It is Well known that silver catalyzes the oxidation of ethylene, by means of air or oxygen, to ethylene oxide. Of the many catalysts proposed for this reaction, only silver has been proved in practice to possess sufiicient activity and selectivity to merit consideration in a commercial operation. However, for successful commercial operation such catalyst must remain active over long periods of use, must be insensitive to changes of tempera ture, and must be relatively insensitive to impurities present in the reactants. Silver metal, used alone, fails to satisfy these requirements. In addition, the conversion of ethylene to ethylene oxide must be high and the formation of by-products, or products of competing reactions must be minimized in order ess be economically attractive. Silver alone produces extremely small yields of ethylene oxide and uneconomically high yields of acetaldehyde, carbon dioxide and water.

Various means have been proposed to overcome these disadvantages, such as incorporating an inert material with the silver, with limited success. Most of these expedients produce a catalyst which suffers from one or more of the disadvantages inherent in the silver alone. In addition, control of the reaction, because of poor heat transfer of the supported catalyst makes the reaction temperature more difiicult to control, resulting in an increased proportion of undesirable products, or requiring complicated reactors with internal cooling facilities. To be commercially acceptable it is preferred that a catalyst be supported on a material which can be utilized in a fluidized condition. Many supports which can be utilized in a thermally ineflicient fixed-bed reactor cannot be satistivity within a reasonable period of operation.

It is, accordingly, an object of this invention to provide a support material for silver such that ethylene oxide can be produced by the direct oxidation of ethylene in its presence and an improved yield obtained thereby. An additional object is to provide a supported silver catalyst which retains maximum activity over long periods, to prothat the manufacturing procduce a high yield of ethylene oxide over a broad range of temperatures, and is not destroyed by accidental exposure to abnormally high temperature. It is a further object of for preparing a supported silver catalyst which can be utilized in a process employing fluidized technique to obtain proper control of the exothermic reaction, and minimize the side and secondary reactions. Other objects of my invention will appear from the further description hereafter.

I obtain the advantages of my invention by incorporating silver with spinel (MgO.Al2O3). The conventional amount of silver is deposited on our support, namely 5 to per cent with the best results being obtained between 4 and 20 per cent.

The temperature of reaction for the process of this invention is between and 400 C. although the normal preferred range is between 250 and 300 C. An important advantage of the supports of this invention is that it stands up well at temperattures above 300 C. Frequently, due to poisoning, the silver catalyst loses its activity but the activity can be restored when the temperature is increased above 300 C. Also misoperation may result in a high temperature which must be withstood by the support. The supports of the prior art are deficient in this respect.

It is also important that the catalytic activity of the support reach a maximum after a short period of operation, in order to increase its usefulness. The supports of this invention are excellent in this respect.

and even impossible to fiuidize.

In order to best fluidize our catalyst and catalyst, particle sizes are important. not be all the same percentage should be small in order to provide a lubricating effect.

The particles should barium peroxide, BaOz, as the promoter.

The support and catalyst may be prepared and used in the article by McBee, Hass, and Wiseman, Industrial and The support material to be tested is first mixed in the support the ti proper proportion and then sized by screening with standard screens of 100-, 200-, and 325-mesh. The difierent particle sizes falling within the above mesh sizes are then mixed with silver oxide and distilled water thereby forming a slurry. The slurry is heated while agitating to a temperature of about 120 C. until the catalyst is thoroughly dried. After such drying, each size of catalyst is rescreened and the desired portions of each size are mixed and the catalyst is ready for use in the fluidized reactor.

The invention can be best understood by referring to the following Working examples.

Spinel corresponding to MgO.Al2O3 but containing as impurities 3 to 4 per cent of SiOz, and 0.5 to 1.5 per cent CaO, was crushed, ground and incorporated with silver as described above. Barium peroxide in the amount of 2.0 per cent was also added. After drying, the silver content was 15.6 per cent and the mixture comprised 35 parts between 100- and ZOO-mesh, 34 parts between 200- and 325-mesh, and 30 parts less than 325-mesh. To a reacif tor suitable for fluidized operation, at a temperature of 276 C. 100 parts of catalyst were introduced along with parts of air and 1 part of ethylene. The reaction products were continuously separated from the catalyst. The

catalyst reached its maximum activity quickly and after 336 hours of operation 79.2 per cent of ethylene was reacted, the conversion to ethylene oxide being 41.7 per cent.

To demonstrate the thermal stability of the support, the temperature was raised to 310 C. for 24 hours and the yield again determined after the temperature reached 276 C. The conversion to ethylene oxide was still the same. After 805 hours of operation 82.3 per cent of: ethylene was reacted, the conversion to ethylene oxide being 42.7 per cent.

Within the limits heretofore set forth, variations in particle size, and temperature results in yields between 35 It and 45 per cent. When a promoter such as barium peroxide is not employed, the yields are from 10 to per cent lower. Variations in silver content have very little effect upon yield.

Having described and illustrated my invention, other embodiments within the scope of the following claims are readily apparent to one skilled in the art.

I claim:

1. A fluidized process for making ethylene oxide comin prising reacting ethylene with oxygen at a temperature between 150 and 400 C. in the presence of a silver oxidation catalyst supported by a magnesium alurninate spine] having a article size distribution comprising to parts between 100- and 200mesh, 30 to 40 parts between 1". 200- and 325mesh, and 10 to 35 parts smaller than 325- mesh.

2. in a fluidized process for making ethylene oxide the improvement comprising reacting ethylene with air in the presence of a silver oxidation catalyst supported by a maganesiurn aluminate spine] at a temperature between 150 and 400 C. and an ethylene to air ratio between 1:5 and 1:2, said support having deposited thereon from 5 to per cent of silver oxide and having a particle size distribution comprising 30 to 40 parts between and 200-rnesh, 30 to 40 parts between 200- and 325-mesh, and 10 to 35 parts smaller than 325-mesh.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A FLUIDIZED PROCESS FOR MAKING ETHYLENE OXIDE COMPRISING REACTING ETHYLENE WITH OXYGEN AT A TEMPERATURE BETWEEN 150 AND 400* C. IN THE PRESENCE OF A SILVER OXIDATION CATALYST SUPPORTED BY A MAGNESIUM ALUMINATE SPINEL HAVING A PARTICLE SIZE DISTRIBUTION COMPRISING 30 TO 40 PARTS BETWEEN 100-AND-200-MESH, 30 TO 40 PARTS BETWEEN 200- AND 325-MESH, AND 10 TO 35 PARTS SMALLER THEN 325MESH. 